Generally if you can feel the teeth on your breast, your position isn't quite right. This is pretty common at that age as you usually don't need to pay as much attention to it - until those teeth get you! When it happens, see how you go with pulling her legs in closer to you so that her chin is touching your breast and her top teeth are further away.

As the others said, it shouldn't last long either, but if your skin gets broken, take care that it doesn't get infected.